This application incorporates by reference Taiwanese application Serial No. 89124031, filed on Nov. 14, 2000.
1. Field of the Invention
The invention relates in general to a planar antenna structure, and more particularly to a planar antenna structure in which the size of a planar antenna is reduced by employing a number of slits on a monopole antenna.
2. Description of the Related Art
As the technology progresses, it makes people""s daily life much easier. In terms of the communication technology, it leads to communication between people almost without the limitation of distance and time. Before, fixed domestic telephones and public telephones were the most commonly used means for communication. They are convenient to use, but they have the disadvantage of lacking mobility. Thus, immediately communicating with people would be impossible in some situations. For this reason, pagers are developed to supplement the requirements of mobile communication. As the time goes by, mobile phones are being substituted for the pagers. Users can immediately make and receive a call by mobile phones. Further, users can even connect to the Internet for browsing information, sending and receiving electronic mails through the use of wireless application protocol (WAP). With these versatile functions, mobile phones are consequently the standard for personal communication equipment. The key to the popularity of mobile phones depends on their compact sizes, innovative functions, and affordable costs. Strictly speaking, the technology of manufacturing circuits determines all of these conditions. If the technology of manufacturing circuits is mature, the relative products can be more compact. In addition, the compact products contribute to their popularity, resulting in mass production and hence lowering the production cost. In this way, how to develop more compact circuitry is an important subject that engineers and researchers greatly concern.
As discussed above, in terms of the integrated circuit development, the current and future trend is towards miniaturization. Thus, wireless communication products are invariably towards this trend. Further, in order to operate in coordination in the whole circuitry, antennas, the key components of the circuitry of wireless communication products, have to be designed to contribute to the needs of miniaturization.
Referring now to FIG. 1, it illustrates the connection of an antenna structure and high frequency circuit. The high frequency circuit 130 may be the internal circuit of a mobile phone, radio transmitter, or radio receiver. The antenna structure 100 can be regarded as the xe2x80x9cwindowxe2x80x9d of the high frequency circuit for transmitting and receiving radio signal. The antenna structure 100 includes a coupling device 110 and antenna 120, in which the coupling device 110 is used to couple the antenna structure 100 with the high frequency circuit 130. When the high frequency circuit 130 requires transmitting signal through the antenna structure 100, the signal is sent to the antenna 120 through the coupling device 110 and is then transmitted. Reversely, when the antenna 120 receives the external signal, it is sent to the high frequency circuit 130 through the coupling device 110 and then signal processing is performed. Thus, the antenna structure 100 is essential for signal transmission and receiving.
In this case, it is desired to have a more compact antenna structure and a circuitry into which the antenna structure 100 and the high frequency circuit 130 can be integrated. If it is feasible to do that, it has the advantage of reducing the complexity of manufacturing circuits as well as reducing the product size, resulting in a reduction of production cost. In addition to a compact antenna structure and integrated design, it is also desired to have an antenna structure combining two antenna structures into one to receive two different signals in order to increase the signals"" intensity. If it is realized, the whole circuit""s functionality is enhanced and the size of the antenna is greatly reduced, resulting in the production cost reduction and the improvement of industrial usefulness. Therefore, some polarization diversity antenna designs have been described in order to realize these purposes. For example, an integral diversity antenna using two orthogonal planar inverted-F antennas is described in specification number U.S. Pat. No. 5,138,328, entitled xe2x80x9cIntegral diversity antenna for a laptop computerxe2x80x9d, and an antenna apparatus using two orthogonal planar inverted-F antennas is described in specification number U.S. Pat. No. 5,420,599. An antenna structure having two orthogonal folded monopole planar antennas is described in specification number U.S. Pat. No. 5,757,333, entitled xe2x80x9cCommunications antenna structurexe2x80x9d. The conventional approaches mentioned above can fulfil the purpose of polarization diversity. However, none of them can lead to a complete integration of the antenna and the circuit into a single circuit broad but to add a radiation metal for the integration. In this way, it increases the complexity of manufacturing the circuits due to the low integration degree, as well as the size of the circuits. As a result, the production cost is greatly increased, reducing the competitiveness of the respect products.
Thus, antenna systems capable of completely integrating the antenna with the printed circuit board are described in specification number U.S. Pat. No. 5,828,346, entitled xe2x80x9cCard antennaxe2x80x9d and specification number U.S. Pat. No. 5,990,838, entitled xe2x80x9cDual orthogonal monopole antenna systemxe2x80x9d, for lowering the complexity of manufacturing circuits. However, they do not mainly concern about downsizing of circuit design and thus the antenna of relative large size is employed. In terms of the trend towards downsizing for circuit design, this large size circuit has no much contribution to the improvement of the products"" competitiveness.
It is therefore an object of the invention to provide an antenna apparatus, integrated with the printed circuit board completely, lowering the complexity of manufacturing circuits and the production cost.
It is another object of the invention to provide a planar antenna structure, which employs a circuit design of downsizing, resulting in a more compact circuit real-estate and more useful in practice as well.
It is still another object of the invention to provide a planar antenna structure, employing the antenna structures to fulfil polarization diversity, resulting in the improvement of the operation performance and the intensity of the received signals. In this way, it improves the characteristic of the entire circuit and enhances the industrial usefilness of the products.
In accordance with the object of the invention, it provides a planar antenna apparatus, which is concisely described as follows.
The planar antenna apparatus includes a monopole antenna. The monopole antenna has a number of slits, where the slits are arranged so that a path through the monopole antenna is formed while the path has sharp turns in alternating directions. In this way, through the arrangement of slits, the excited surface current""s path is extended so that the monopole antenna operates at a lower frequency. Therefore, the monopole antenna is a reduced one as compared with the monopole antenna without slits operating at the same frequency. In addition, two ground conductors are mounted on either side of the monopole antenna, where ground conductors are apart from the monopole antenna respectively. As such, there is a coplanar waveguide (CPW) effect among the ground conductors and the monopole antenna, leading to the entire antenna apparatus presenting almost good input-impedance matching. Finally, a coupling device, such as microstrip line or coaxial line, feeds the monopole antenna so as to transmit and receive signals.
The planar antenna apparatus can further be employed, fulilling the purpose of polarization diversity. During implementation, one can adopt two antenna apparatuses mentioned above to be mounted in different directions, such as in perpendicular directions. In the case of the two antenna apparatuses with slits perpendicular to one another, the excited surface currents of the antennas flow in directions perpendicular to each other. As a result, the polarization planes and both E-plane and H-plane patterns of the two antennas are perpendicular to one another. Thus, the purpose of polarization diversity is fulfilled.